A store window display in Rome. Click to enlarge.
The answer is, "You dream in English."
When you think about it, you can't sing "I'm Dreaming of a White Christmas" in Italian, can you? (Look at the picture.) The song won't rhyme.
The creator of this store window display in Rome agrees. He/she knows that you don't mess with tried and true slogans and lines from Christmas songs. (Try singing, "Here Comes Suzy Snowflake" in Italian.)
They have a different approach in Asia, though, where anything goes. Look at a couple of examples of Christmas sloganry on www.engrish.com. example A - example B